1. Field of the Invention
The present invention relates to a sheet conveying apparatus for conveying sheets.
2. Description of the Related Art
The sheet conveying apparatus used for an electrophotographic apparatus conveys and guides a sheet by a guide unit.
The guide unit uses a plate-shaped member made of metal or plastic. When the guide unit is a flat plate, contact resistance with a sheet is large, which increases frequency of jamming. Thus, to reduce conveying resistance which causes jamming, many ribs are disposed in a guiding surface of the guide unit to improve sheet guiding performance.
Regarding the ribs arranged in the guide unit, there are ribs pushed wide in a sheet width direction toward a downstream side in a sheet conveying direction (discussed in Japanese Patent Application Laid-Open No. 2001-315993).
As discussed in Japanese Patent Application Laid-Open No. 2001-315993, when the ribs are disposed to be pushed wide in the sheet width direction toward the downstream side of the sheet conveying direction, areas of the sheet that contacts with the convey ribs are dispersed without concentrating in one spot in the width direction. Thus, surfaces of the convey ribs give little damage to the sheet. On the other hand, when the ribs are disposed to be pushed wide in the sheet width direction toward the downstream side of the sheet conveying direction, a plurality of rib start points (rib conveying-direction upstream ends) has to be provided in the sheet conveying direction. The rib start points and the conveyed sheet come into point-contact with each other, which concentrates a rubbing force. The concentration of the rubbing force between the sheet and the rib start points may cause damage to a surface of the sheet. In other words, when the ribs are tilted with respect to the sheet conveying-direction, while the surface of the convey ribs give little damage to the sheet, rib start points cause damage to the sheet. If the ribs are arranged parallel to sheet conveying-direction, a number of rib start points can be reduced, however, the surface of ribs causes damage to the sheet. While the problem occurs in the case in which the ribs are tilted with respect to the sheet conveying-direction, the contradictory problem occurs in the case in which the ribs are arranged parallel to sheet conveying-direction contradict each other.
A thermal content of thick coated paper is large immediately after a toner image is fixed on the sheet by heat, the sheet, given heat during the fixing, is conveyed in a very hot state. In consequence, while not fixed on the sheet, toner is brought into contact with the rib start points of the guide unit disposed in a conveying path in a soft state, and it is highly possible that rib traces are left or uneven gloss appears as damage.